Correct, from the “How Does It Work?” section:
WinBoat is an Electron app which allows you to run Windows apps on Linux using a containerized approach. Windows runs as a VM inside a Docker container, we communicate with it using the WinBoat Guest Server to retrieve data we need from Windows. For compositing applications as native OS-level windows, we use FreeRDP together with Windows’s RemoteApp protocol.
It probably depends on what virtual machine approach you take.
I prefer the virtual machine approach (QEMU/KVM) with the looking glass client. This means pretty much native draw speeds.
This also means not needing your old Windows install - you just need one in your virtual machine. Just the same as you have with WinBoat.
I’ve posted a couple of videos, let me link them again here, since this is a long thread and it may be hard to find quickly 
the first video
and another with 3 Rhino instances doing heavy (raytracing) work.
(Note the wobbly Linux windows for added productivity boost)